. >> at white house today president obama called the bombings an act of cowardice and made plans to travel to boston on thursday. >> what we don't yet know is who carried out the attack or why. whether or not planned and executed by a terrorist organization foreign or domestic or was the act of a malevolent individual. >> the president ordered flags at half staff in memory of the victims. >> bay area people who attended or competed in the marathon are getting back home now. we've been speaking with many of them today. wayne freedman has the coverage. >> we like to say every person has a story. but travelers arrived from san francisco international airport today only one story mattered in so many different versions. >> loud loom. >> two block as head. >> thought it's a cannon. >> people started to run one way. emts going another way. no one knew what is going on. >> you see snok smoke. you know there is chaos. >> there is no getting away from them. after flying across a continent. >> this is pretty emotional. an 8-year-old boy, they came out and watched and knowing that that could have been